Supervenience Thesis, Valid or Not?

For those interested in cognitive science, the supervenience thesis seems to be one of those fundamental axioms which goes unsaid. If it needs to be said however, I think Tim Maudlin1 summed it up best:

Of course, the thesis that physically identical brains would support phenomenally identical states of consciousness is not analytic. But some such physicalist assumption underlies all contemporary research into perception and neuro-physiology. Furthermore, it seems to be an essential thesis for the computationalist. For computational structure supervenes on physical structure, so physically identical brains are also computationally identical. Hence, any mental property that can be given a purely computational analysis ought to be shared by physically identical brains.

In sequel, a somewhat stronger claim about supervenience shall be employed. States of awareness and sensory events take place in time; they are fairly precisely datable. One can assert that Sam had a toothache at 12:05 or that Sheila spent five minutes wondering about Fermat’s last theorem. A natural, indeed nearly inescapable, explanation for this is that conscious events and episodes supervene on concurrent physical events and processes. One’s phenomenal state at a time is determined entirely by one’s brain activity at that time. Hence, two physical systems engaged in precisely the same physical activity through a time will support the same modes of consciousness (if any) through that time. Let us call this the supervenience thesis.

Seems that all other philosophers have the same views of supervenience, and in fact, the term has a unique meaning in philosophy. Philosophers widely accept that phenomenal properties supervene on physical properties. Most however, don’t refer to this as the “supervenience thesis” but simply as supervenience.

The core idea of supervenience is captured by the slogan, “there cannot be an A-difference without a B-difference.” It is important to notice the word ‘cannot’. Supervenience claims do not merely say that it just so happens that there is no A-difference without a B-difference; they say that there cannot be one. A-properties supervene on B-properties if and only if a difference in A-properties requires a difference in B-properties—or, equivalently, if and only if exact similarity with respect to B-properties guarantees exact similarity with respect to A-properties.

Ok, so that sounds easy enough. The obvious example would be that A represents mental or phenomenal states and B represents physical states, though the terminology can be used also for other, less controversial concepts. However, there are obvious issues that arise when we apply this concept, such as:

But there is vigorous disagreement about whether the supervenience relation holds with metaphysical or merely nomological necessity. Ask yourself—could there be an individual that has no conscious experience at all, despite being physically indiscernible from an individual that is conscious (Kirk 1994; Chalmers 1996)? That is, could there be what philosophers call a ‘zombie’? Because it is widely agreed that the mental nomologically supervenes on the physical, it is widely agreed that zombies are nomologically impossible—that their existence would violate psychophysical laws.

And also the problems with mental causation:

Some think that supervenience is indeed ontologically innocent in this sense. After all, if the A-properties supervene with metaphysical necessity on the B-properties, then they come along automatically given the B-properties. To borrow Kripke's metaphor (1972, 153-154), once God fixes the B-properties, she is all done; she does not need to do anything further to get the A-properties going. Indeed, she cannot block them. Given the distribution of B-properties, there is no further question about which A-properties are instantiated. So, it is claimed, the latter are nothing over and above the former. However, other people vigorously resist this idea. How can the A-properties not count as a further ontological commitment, if they are numerically distinct from the B-properties?
This dispute is central to various issues in metaphysics and the philosophy of mind. For example, nonreductive physicalists often say that mental properties are distinct from but nonetheless “nothing over and above” physical ones. Their reductivist opponents, however, clearly think that this is illegitimate. This can be seen in the charge that nonreductive physicalists face the exclusion problem—that they are unable to account for the causal efficacy of the mental without claiming that all of its effects are “double-caused.”

For those interested in cognitive science, the supervenience thesis seems to be one of those fundamental axioms which goes unsaid. If it needs to be said however, I think Tim Maudlin1 summed it up best:

Seems that all other philosophers have the same views of supervenience, and in fact, the term has a unique meaning in philosophy. Philosophers widely accept that phenomenal properties supervene on physical properties. Most however, don’t refer to this as the “supervenience thesis” but simply as supervenience.

Ok, so that sounds easy enough. The obvious example would be that A represents mental or phenomenal states and B represents physical states, though the terminology can be used also for other, less controversial concepts. However, there are obvious issues that arise when we apply this concept, such as: